/*
 * Copyright (c) 2001, 2003, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 *
 *
 *
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 */

package com.sun.corba.se.impl.orbutil;

import java.util.EmptyStackException;

// We implement a Stack here instead of using java.util.Stack because
// java.util.Stack is thread-safe, negatively impacting performance.
// We use an ArrayList instead since it is not thread-safe.
// RequestInfoStack is used quite frequently.
public class StackImpl {
    // The stack for RequestInfo objects.
    private Object[] data = new Object[3];
    private int top = -1;

    // Tests if this stack is empty.
    public final boolean empty() {
        return top == -1;
    }

    // Looks at the object at the top of this stack without removing it
    // from the stack.
    public final Object peek() {
        if (empty())
            throw new EmptyStackException();

        return data[top];
    }

    // Removes the object at the top of this stack and returns that
    // object as the value of this function.
    public final Object pop() {
        Object obj = peek();
        data[top] = null;
        top--;
        return obj;
    }

    private void ensure() {
        if (top == (data.length - 1)) {
            int newSize = 2 * data.length;
            Object[] newData = new Object[newSize];
            System.arraycopy(data, 0, newData, 0, data.length);
            data = newData;
        }
    }

    // Pushes an item onto the top of the stack
    public final Object push(Object item) {
        ensure();
        top++;
        data[top] = item;
        return item;
    }
}
